Adds root directive to vhost_header and vhost_ssl_header templates.

This change will result in there being a 'root' directive in both the
server block, and the location sub-block. This is a perfectly valid
configuration and avoids the possible issue of having a location
with no 'root' if it isn't explicitly set.
Tidy up on the www_root fixes

Drops the explicit ''defined?'' check as suggested by jfryman, and clears some pointless whitespace.
Missing 'if' in vhost_header.erb